Conventionally, in the field of lens production, the techniques to obtain optical lenses with high heat-resistance by preparing lens sections formed of curable resin on a glass substrate have been studied. As an example of a production method of an optical lens employing the technique, there has been proposed a method of forming a so-called “wafer lens” that lens sections as molded bodies of curable resin, for example plural refractive lenses, are formed on a surface of a glass substrate, and of cutting the glass substrate together with the lens sections after that.
As a production method of a wafer lens, there is provided, for example, a method of using two intermediate dies such that a first intermediate die (sub-master) made of resin is molded by a die (master), a second intermediate die (sub-sub-master) also made of resin is subsequently molded by the first intermediate die, and a wafer lens made of resin is produced by using the second intermediate die (for example, see Patent Literature 1 and 2). Especially, Patent Literature 2 discloses a so-called step-and-repeat method wherein lens sections are formed successively on a glass substrate with a large diameter.
The method of producing a wafer lens by using two intermediate dies will be described below.
FIGS. 28a and 28b show a method of producing first intermediate die 8G from die 7G. At first, as shown in FIG. 28a, resin 84H is dripped on the upper surface of die 7G which includes molding section 71G having a negative shape corresponding to a shape of an optical surface of convex lens section 11G (see FIG. 30b) of wafer lens 1G (a dispensing step). Then, a first area as a part of first intermediate-die substrate 80G is positioned over die 7G to be in a sucked and stationary condition. After that, first intermediate-die substrate 800 is moved down toward die 7G which has been arranged at a lower position, to press resin 84H against the first area of first intermediate-die substrate 80G (an imprinting step). At that time, in order to avoid flat section 72G which is arranged around molding section 71G of die 7G to connect with the molding section 71G from hitting first intermediate-die substrate 80G, first intermediate-die substrate 80G is stopped to form a constant gap S4 between die 7G and first intermediate-die substrate 80G. The amount of gap S4 in FIG. 28a is assumed to be ΔH. The amount ΔH is not only an amount required to mechanically avoid the hitting, but also is an amount determined in consideration of securing a minimum gap required in view of molding resin 84H. After that, while the position in height of first intermediate-die substrate is kept as it is, resin 84H filling molding sections 71G is irradiated with light from an upper position of first intermediate-die substrate 80G to be hardened with light (an exposure step). Then, while first intermediate-die substrate 80G is moved upward, resin 84H is released from die 7G (a die-releasing step). After that, die 7G is shifted by a predetermined amount as shown in FIG. 2, the above dispensing step, imprinting step and exposure step are performed at the prescribed position (corresponding to a second area of first intermediate-die substrate 80G), and these steps are repeated to perform a molding process in the so-called step-and-repeat method. Employing such the structure brings the advantage that a molding die covering a broad area can be molded with a small die.
However, when such the molding process using the step-and-repeat method is employed, gap X of the prescribed amount is generated between the first area and the neighboring second area after the molding process at the first area, as shown in FIG. 2. It is generated because the positions of the first area and the neighboring second area cannot be matched with perfect accuracy in position.
As the result, first intermediate die 8 including groove section 86G in which the ground of first intermediate-die substrate 80G shows, on the bottom surface of first intermediate-die substrate 80G, is produced, as shown in FIG. 28b. It is caused because resin 84H does not go there.
Further, when a first intermediate die is molded with a die, a second intermediate die is molded with the first intermediate die, and an optical element is molded with the second intermediate die, by employing such the step-and-repeat method, the following structures are provided.
FIGS. 29a and 29b show a method of molding second intermediated die 9G with first intermediate die 8G. As shown in FIG. 29a, resin 9411 is dripped on the upper surface of first intermediate die 8G (a dispensing step). Then, second intermediate-die substrate 90G is positioned over first intermediate die 8G to be in a sucked and stationary condition. After that, second intermediate-die substrate 90G is moved down toward first intermediate die 8G which has been arranged at a lower position, to press resin 94H against second intermediate-die substrate 90G (an imprinting step). At that time, in order to avoid the most projecting part of resin section 84G of first intermediate die 8G from hitting second intermediate-die substrate 90G, first intermediate die 8G is stopped to form gap S5 of the amount of ΔH between first intermediate die 8G and second intermediate-die substrate 90G. After that, the exposure step and the die-releasing step are similarly performed, and second intermediate die 9G including molding sections 91G on the bottom surface of second intermediate-die substrate 90G can be produced, as shown in FIG. 29b. Herein, sign 93G represents a part where resin 94H entering groove section 86G of first intermediate die 8G is hardened, and the part is highest in resin section 94G of second intermediate die 9G.
FIGS. 30a and 30b show a method of molding wafer lens 1G as an end product with second intermediate die 9G. As shown in FIG. 30a, resin 4H is dripped on the upper surface of second intermediate die 9G (a dispensing step). Then, glass substrate for a wafer lens is positioned over second intermediate die 9G to be in a sucked and stationary condition. After that, glass substrate 2G is moved down toward second intermediate die 9G which has been arranged at a lower position, to press resin 4H against glass substrate 2G (an imprinting step). At that time, in order to avoid the most projecting part of resin section 94G of second intermediate die 9G from hitting glass substrate 2G, second intermediate die 9G is stopped to form gap S6 of the amount of ΔH between second intermediate die 9G and glass substrate 2G. After that, the exposure step and the die-releasing step are similarly performed, and wafer lens 1G can be produced as shown in FIG. 30b. As the result, the height of flat section 12G formed around convex lens section 11G and connecting the convex lens section 11G of wafer lens 1G is 2ΔH from glass substrate 2G, which is twice of gap ΔH being required for avoiding the hitting in one molding processing described above.
In other words, the situation that groove section 86G of the first intermediate die is formed, is a cause of the situation that gap ΔH, which is required when the second intermediate die is formed with the first intermediate die, grows into the twice amount of gap when a lens is finally formed with the second intermediate die.